MICROEARTHQUAKE TOMOGRAPHY INVERSION USING LOTOS ALGORITHM TO DELINEATE FLUID SATURATION ZONE IN THE DIENG GEOTHERMAL FIELD, CENTRAL JAVA

• Main Author: Albert Mogi, Phillip
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/87140
• Institution: Institut Teknologi Bandung

Microearthquake (MEQ) surveys are essential instruments for managing geothermal resources, as they can identify permeable zones and evaluate the potential, magnitude, and impact of earthquakes on geothermal fields. The distribution of microearthquakes helps differentiate reservoir types characterized by fluid saturation zones. The Local Earthquake Tomography Software (LOTOS) algorithm will be used to determine reservoir conditions by collecting data on recorded seismic wave phases. The LOTOS algorithm features a user-friendly interface, particularly for beginners, integrating one-dimensional modelling, source identification, and threedimensional tomography with ray bending. The LOTOS algorithm has not yet been used in geothermal field research. Therefore, it is employed to create a seismic velocity model and identify fluid saturation zones in the Dieng geothermal field, where tomographic research is still limited. Microearthquake data was acquired from May 2, 2021, to July 29, 2022, using 18 station locations in the Dieng Geothermal Field that documented microearthquake (MEQ) data. The travel times of P and S waves from 1556 seismic events, along with station coordinates from the catalog, will be used to develop the velocity model and tomogram of the Dieng geothermal field reservoir. The LOTOS algorithm was successfully executed using microearthquake data, as evidenced by the results of the Checkerboard Resolution Test (CRT), which show good resolution in the production area of the Dieng geothermal field from an elevation of 1.5 km down to -1 km and -2 km in some places. CRT results are used to interpret tomography outcomes. There are indications of two reservoirs: the Pagerkandang reservoir in the northwest at an elevation of 0 km and the Pakuwaja reservoir in the southeast at an elevation of 0.5 km. Both reservoirs are waterdominated, as indicated by relatively low P and S wave velocities and a high Vp/Vs ratio (>1.7).